1. Field of the Invention
The present invention relates to the detection of electric fields, and more particularly, to a method and apparatus for determining potentially hazardous energized objects.
2. Description of the Related Art
Power distribution systems, for example those in large metropolitan areas, are subject to many stresses, which may occasionally result in the generation of undesirable or dangerous anomalies. An infrequent but recurrent problem in power distribution infrastructures is the presence of “stray voltages” in the system. These stray voltages may present themselves when objects, such as manhole covers, gratings, street light poles, phone booths, and the like, become electrically energized (e.g., at 120V AC). These objects may become energized when an electrically conductive path is established between underground secondary cabling and these objects, for example, due to physical damage to electrical insulation that results in direct contact between electrically conductive elements, or through the introduction of water acting as a conductor. These energized objects present obvious dangers to people and animals in the general public.
In order to identify energized objects throughout a large area, such as a large urban area, a mobile system may be utilized to traverse the area and remotely (i.e., in a non-contact manner) detect stray voltages on energized objects. One technique for detecting such stray voltages is by measuring the electric field pattern exhibited by energized objects at the fundamental power line frequency (e.g., 60 Hz in the U.S., 50 Hz in Europe and parts of Asia).
During the remote detection of stray voltages, a “false positive” may occur when an object emits an electric field pattern resembling that of a potentially hazardous energized structure while not being energized in a fashion that could cause shock or electrocution. For example, a “Don't Walk” pedestrian crossing signal often employs LED's that emit an electric field pattern similar to that of a potentially hazardous energized structure even though the LED's and their electrical connections are well protected from contact and no shock hazard exists. Discriminating between potentially hazardous energized structures and these false positives requires a technician operating a mobile detection system to stop and make time-consuming manual inspections of the structure.
Therefore, there exists a need in the art for efficiently discriminating between potentially hazardous energized objects and potentially non-hazardous sources of electric field.